Method of the preparation of fibrillar and lamellar porous microstructures and nanostructures by means of controlled vacuum freeze-drying of liquid nanoparticles dispersions

Abstract

The invention relates to a method of preparation of lamellar porous microstructures and nanostructures of various density based on controlled vacuum freeze-drying of a liquid dispersion of nanoparticles. The liquid dispersion of particles is rapidly freezed into solid state inside a tightly closed volume. In this form it is submitted to vacuum freeze-drying with required rate of sublimation of molecules of a liquid dispersion medium, until their total removal, accompanied by the creation of lamellar microstructures and nanostructures. The orientation of the normal vector of the dominant surface of sublimation interface can be set with regard to the required properties of the final sublimate structure from vertically upwards to vertically downwards. The sublimation rate is adjusted by combination of vacuum depth and external heating of the sublimation interface of the frozen material.

The invention claimed is: 
     
       1. A method of preparing lamellar nanostructural materials by controlled freeze-drying of a liquid dispersion of nanoparticles or submicron particles, the method comprising:
 a) rapidly and isotropically freezing a liquid dispersion of nanoparticles or submicron particles in a dispersion medium inside a closed space to form a solid state dispersion; and 
 b) freeze-drying the solid state dispersion, where the molecules of the dispersion medium are removed at a rate of sublimation, wherein the rate of sublimation is selected such that the rate of regression of a sublimation interface of the solid state dispersion is between 10 −2  μm/s and 10 2  μm/s at a reduced pressure value in the range of between 10 kPa and 1 Pa and a temperature of between −130° C. and 0° C., until the entire dispersion medium is removed by sublimation; wherein the normal vector of the predominant surface of the sublimation interface is oriented such that:
 i) the normal vector is between 0° and 45° relative to the upward vertical direction, resulting in multi-bonded lamellar aggregates; or 
 ii) the normal vector is between 135° and 180° relative to the upward vertical direction, resulting in simple lamellar aggregates. 
 
 
     
     
       2. The method according to  claim 1 , wherein the liquid dispersion comprises fullerene nC 60  aggregates and demineralized or distilled water, the step of freeze-drying occurs at a reduced pressure of about 24 Pa and a surface temperature of-about −24° C., and the normal vector of dominant sublimation interface surface points vertically upwards, so that all the water sublimates into a freezing area of the freeze-dryer.